The present invention relates to an apparatus for transmitting an optical image whereby an image guide consisting of a number of bundled optical fibers and an optical lens system are combined and a two-dimensional image is transmitted from one location to another location. For example, the invention can be used for observation, inspection, etc. of nuclear facilities from a distant place.
Conventional technology and its problems will be described with reference to FIGS. 1 to 6. A fundamental constitution of the optical image transmitting apparatus which is constituted by a combination of the image guide consisting of a number of bundled optical fibers and the optical lens is shown in FIG. 1 (refer to W. B. ALLAN, Fiber Optics, Theory and Practice, 1973, p. 149, FIG. 1). In this optical system, an optical image is transmitted in the manner as follows. An image 11' of an object 11 is first formed on an edge surface 13' of an image guide 13 by an objective lens 12. The image guide 13 is constituted by bundling a number of optical fibers 13a, 13b, 13c, . . . Among the light formed on the edge surface 13' of the image guide 13, the light which entered the core section of each optical fiber constituting the image guide is transmitted to a rear edge surface 13" of the image guide 13. In FIG. 1, it is illustrated that the edge surface 13' and the rear edge surface 13" of the image guide 13 are arranged rectilinearly on the same axis. However, in an actual apparatus, a length of the image guide 13 is ordinarily tens of meters and in such a case it is apparent that the image guide can be freely bent at locations intermediate the edge surfaces.
The image transmitted onto the rear edge surface 13" of the image guide 13 is constituted by the light and shading of the point corresponding to the core section of each optical fiber of the image guide 13. The image transmitted onto the rear edge surface 13" is observed as an image 15 by an ocular lens 14 on a screen disposed at the rear location. The image 15 is constituted by points 15a, 15b, 15c, . . . , and the like corresponding to the optical fibers which constitute the image guide 13. When the edge surface 13' of the image guide 13 was projected on the object 11 by the objective lens 12, the location on the object 11 represented by these respective points corresponds to the location where the core section of each optical fiber at the edge surface 13' is image-formed.
However, the optical image transmitting apparatus with the conventional arrangement shown in FIG. 1 has the following problem. Namely, the image 15 obtained by the image guide optical system of FIG. 1 is represented by the light and shading of the point corresponding to the core section of each optical fiber which constitutes the image guide as shown in FIG. 2 which illustrates an example thereof. Therefore, there is a problem such that the resolution of the image is restricted by the number of optical fibers of the image guide, so that the resolution is small.
As one method of solving such a problem, a method whereby the edge surface 13' and the rear edge surface 13" of the image guide 13 are synchronously vibrated is known. However, this method has a problem such that the apparatus increases in size and its reliability is low since there is a movable section.
As another method, a method whereby dispersive devices are arranged in the objective lens system and ocular lens system, respectively, has been proposed (Japanese Patent Application Laid-Open Publication No. 23653/71, "APPARATUS FOR TRANSMITTING OPTICAL IMAGE"). FIG. 3 shows an arrangement of the image guide optical system using the dispersive devices. In FIG. 3, a reference numeral 31 denotes an object; 32, 34 are objective lenses; and 33 a dispersive device disposed between the objective lenses 32 and 34. A numeral 35 indicates an image guide which is formed by bundling a number of optical fibers such that their edge surfaces are regularly aligned, and 35a represents one of the optical fibers. Numerals 36 and 38 are ocular lenses; 37 is a dispersive device which is disposed between the occular lenses 36 and 38 and 39 is an image on the screen which is transmitted by this optical system and is constituted by respective points 39a, 39b, 39c, . . . , etc.
In FIG. 3, the image 39 is represented by the points corresponding to the respective optical fibers which constitute the image guide 35. When an edge surface 35' of the image guide 35 was projected onto the object 31 by the objective lens system, these points represent the light at the location where the optical fiber core section of the image at that edge surface is formed.
The operation of one optical fiber 35a among the optical fibers which constitute the image guide 35 will now be discussed. First, the case where the object is illuminated by blue light is considered. In this case, the point on the object 31 to which the optical fiber 35a transmits the light can be known as a location 31a where the image corresponding to 35a is formed by forming the image of 35a onto the object 31 by the objective lens systems 32, 33 and 34. The point corresponding to 31a among the points which constitute the image 39 is 39a.
The case where the object is illuminated by the green light will now be considered. In this case as well, the point on the object 31 to which the optical fiber 35a transmits the light can be known by the similar means as mentioned above. However, in this case, since the light is green, the progressing direction of the light is slightly more bent by the dispersive device 33 than in the case of blue light, so that the image of 35a is formed at a location 31b which is slightly different from the location in the case of blue light. Therefore, in case of using green light, the point to which the light is transmitted by the optical fiber 35a is 31b. The progressing direction of the light is also bent by the dispersive device 37 even in the ocular lens system; thus, the image responsive to the point 31b on the object 31 is formed at the point 39b different from the case where the blue illumination light was used. In case of using red light as the illumination light also, the light at a point 31c on the object 31 is transmitted to the point 39c by the optical fiber 35a due to the similar reason.
In this way, the use of the dispersive devices enables the lights of the points at a few locations to be transmitted by one optical fiber. The similar operation also occurs with regard to each optical fiber which constitutes the image guide 35. FIG. 4 illustrates the states of the points which constitute the image 39 which is transmitted by the image guide optical system in this case. In FIG. 4, numerals 39a, 39b and 39c indicate the points to which the lights are transmitted in the case where the blue, green and red illumination lights were used, respectively.
If the white light is used as an illumination light, the points to which the light is transmitted by a single optical fiber will become continuous since the white light continuously includes blue, green, red, . . . , etc. Therefore, the image obtained is constituted by a short line instead of a set of points. In this case, it can be considered that the image at the edge surface of the optical fibers is closely arranged in the longitudinal direction of the short line; as a result, the resolution in the longitudinal direction of the short line is improved.
FIG. 5 illustrates the state of the short lines which constitute the image in such a case. In FIG. 5, a numeral 51 denotes a short line constituted by the sequential points to which the light is transmitted by a single optical fiber. As an extent of dispersion by the dispersive devices 33 and 37 increases, a length of the short line 51 becomes long, so that the short line will partially overlap with the short lines by the adjacent optical fibers. FIG. 6 shows the state in the case where the adjacent short lines partially overlapped. A numeral 61 indicates an overlapped portion. The brightness information at the overlapped portion is transmitted by two optical fibers. Therefore, even if one of the two optical fibers is burned out, the brightness information is transmitted by the other optical fiber. Consequently, the lack of brightness information at the overlapped portion due to the burn-out of the optical fiber is avoided.
As described above, use of the image guide optical system whereby the dispersive devices are arranged provides an advantage such that the resolution is improved as compared with the case where no dispersive device is used since the lights at many points are transmitted in the direction of the short line which constitutes the image. Further, in the case where the short line is elongated like a straight line with the overlapped portion, as well as the above advantage, there is also an advantage such that it is possible to prevent the lack of brightness information even if the optical fiber is burned out.
However, in the foregoing arrangement, there is a problem such that the resolution in the direction perpendicular to the direction of the short line or straight line which constitutes the image is not improved. In addition, even in the case where the short lines are continuously formed to derive the straight line with overlapped portions, a length of the portion which is not overlapped is restricted by the distance between the adjacent two optical fibers in its rectilinear direction, so that there is a problem such that it is impossible to improve the resolution any more.